It is well known to combine different color light sources to enable a variable color output. By independently controlling three primary color light sources, a range of output colors may be generated. Typically, each light source is provided with a separate driver. Such kind of individual driving is for example disclosed in WO2014/103666.
There are also lighting systems in which two different color light sources are combined. While this does not enable full color control of the output color, it does enable various lighting effects to be obtained. For example, by combining white and red LED strings, color temperature dimming is possible, by which the color temperature is varied as a function of the dimming level.
In order to reduce cost, it would be desirable to use a single power conversion stage in systems with such color temperature dimming such as light emitting diode (LED) based luminaires.
There have been proposals for cost-effective power converters, using hybrid converters which combine switched capacitor converters (SCC) and switched inductive converters. These types of converter provide efficient high switching frequency operation, reduced size and reduced complexity. The current mode control makes them especially suitable for LED based lighting applications.
For example, WO 2015/040575 discloses the use of this type of hybrid switched capacitor converter design to drive two different LEDs in order to achieve blackbody dimming, in which the color point varies as a function of the dimming level. In WO 2015/040575, the two LEDs are in a separate parallel configuration, and the converter delivers two independent output voltages, each associated with a separate output filter. There is therefore still duplication of some components. Further, an extra controllable voltage regulator is also used to adjust the voltage to the switched capacitor converter.